Syntheses of medium-sized cyclic ethers from carbohydrates via an intramolecular nitrile oxide-alkene cycloaddition strategy

Theregioselectivity of intramolecular 1,3-dipolar cycloadditions of nitrile oxides prepared from 3-O-alkenyl-1,2-O-isopropylidene-α-D- pentodialdofuranoses is dependent on the length of the alkenyl chain. 3-O-Homoallyl nitrile oxide afforded exo-cyclization oxepane exclusively. 3-O-Pentenyl nitrile oxide produced a mixture of exo- and endo-cyclization adducts (oxocane and oxonane) whereas 3-O-hexenyl, heptenyl, and octenyl oxides all gave endo-cyclization adducts (ten-, eleven-, and twelve-membered cyclic ethers, respectively) exclusively.